"Most people feel the principles of the Democratic Party require you to be a Democrat," Mr. Rothenbuhler said.

Mr. Tucker said the AFL-CIO group will help Mr. Collins by door-to-door canvasses, phone calls, direct mail, and work-site leafletting, the same commitment that was made to Ms. Lopez. The AFL-CIO affiliates include building trades unions, American Federation of State County and Municipal Employees, Toledo Federation of Teachers, and the Toledo police officer and firefighter unions.

Mr. Collins, a retired police officer and former head of the city police officers' union and current district city councilman, said he was "humbled but proud to have the support of the men and women who are members or lead respective bargaining units in our area."

The AFL-CIO said the Toledo mayor race is a top priority. Mayor Bell earned the wrath of labor unions with his support in 2011 of a failed Republican-backed bill to weaken public sector collective bargaining rights, known as Senate Bill 5/Issue 2.

The Bell campaign said the lineup of labor unions supporting Mr. Collins is not a surprise.

"As mayor, Mike Bell has needed to make some difficult decisions in order to move the city forward, and endorsements like this are the result of those decisions. We will take Mike Bell’s record of success directly to the voters with energy. We believe that when voters compare the records of the candidates — on reducing the city’s deficit, creating an environment for job growth, hiring police officers and fire fighters and reducing crime — they will choose Mike Bell to continue to lead the city," spokesman B.J. Fischer said.